The present invention relates to the application of machine vision algorithms in the manufacture of semiconductor devices. Specifically, the invention applies to automatic detection and analysis of geometric patterns on the surface of interconnection lands, or pads, of integrated circuits, or semiconductor devices. Semiconductor devices are more recently being designed and fabricated with pads having multiple regions or zones that appear as a series of concentric geometric patterns. Automatic detection and analysis of multiple zones of pads of semiconductor devices is useful in various methods of semiconductor device fabrication, including, for example, in a probe mark inspection operation. A probe mark inspection operation is typically performed subsequent to an electrical testing operation of the semiconductor device, to ascertain that mechanical probe marks exist, indicating that an electrical test has been performed. The use of an apparatus that can automatically detect and analyze probe marks on device lands can be more reliable and accurate than manual inspection with the human eye.
Silicon device fabrication involves various circuit definition steps with chemical processing of a wafer containing an array of multiple devices. An electrical test of the wafer is typically employed to identify defective devices and/or to perform process control. The electrical test is performed by probing the wafer with needle-tipped probes, leaving an indentation or surface finish aberration on the pad where the probe made contact with the pad. An inspection of the mark left by the electrical testing probe may be performed subsequent to the electrical test to visually assess the electrical testing operations. Absence of a mark, or misalignment of the mark on the pad, would indicate that the test was not properly performed. Additionally, data collected from a probe mark inspection may be useful in process characterization and process control of equipment alignment parameters.
Probe mark inspection, as described in the commonly assigned U.S. patent application Ser. No. 10/032,168, entitled “Probe Mark Inspection Method and Apparatus,” filed Dec. 21, 2001, incorporated by reference herein, is a useful operation in silicon device fabrication because of the increasing size, density, and value of the silicon wafers. Good devices must not be falsely identified as defective, whereas defective devices must be accurately identified so that needless processing and packaging effort is not further expended. Verification of the integrity of the electrical testing operation ensures that the devices are properly tested to avoid the cost penalties of false or improper indictment. Further, human visual inspection using a microscope is not only extremely tedious, but human operators performing inspection can actually introduce particulate contamination in a cleanroom environment that may impair processing yield. Thus, the operation is ideally suited for a computer-assisted machine vision application.
Probe mark inspection of semiconductor device pads having multiple zones may be performed differently for different zones of the pad. The inspection operation could be performed on the entire pad by ignoring the multiple zones, or restricted to only one zone or region comprising a portion of the pad, with reliable and useful results. The dimensions and position of the various pad zones is therefore a useful input to the inspection.
Currently, the various multiple zones or regions of a semiconductor device pad can be manually specified by an operator of an inspection apparatus. Geometric pattern matching tools, such as PATMAX® from Cognex Corporation, can be used to register, detect, and/or analyze zone boundaries of multiple zone pads, but such tools can be ineffective if the actual pad has more zones than the trained model. Additionally, the geometric pattern matching tools are typically not reliable due to extremely weak zone boundaries exhibited in a typical image of a pad.
For the foregoing reasons, there is a need for a machine vision apparatus that can automatically determine the geometry of multiple zones or regions of semiconductor device pads, in conjunction with a machine vision inspection operation to quickly and reliably assess the presence of a probe mark.